--- Master Handbook Of 1001 Practical Electronic Circuits Pdf Updated Jun 2026

A photoresistor triggers a comparator (usually an LM311) to turn on an LED when dark. "Hysteresis" prevents flickering. This circuit is the intellectual parent of every modern dusk-to-dawn streetlight.

Page 512 now showed a different circuit. The same components, but the traces curved in impossible ways—lines that crossed without connecting, capacitors drawn as open eyes. The text beneath read: Circuit 512b: Receiver for Frequencies Below Silence. A photoresistor triggers a comparator (usually an LM311)

Replace the LDR with a phototransistor (BPW77NA) for faster response, and swap the 2N3906 for a MOSFET (2N7000) to handle more relay current. A photoresistor triggers a comparator (usually an LM311)